Implement inline children data atoms

[JonathanMace]

For child data with index < 15, it is cheaper to inline the child as a data atom.

[JonathanMace]

One question is whether you can have an inline child followed by a non-inline child followed by an inline child. Yes, this is OK; the way you do it is by having duplicate bag headers, and having the second bag header between the non-inline child and the next inline child.